U.S. Pat. No. 5,801,758 teaches a videoconferencing system with a bidirectional screen, that is, a screen through which images can be both captured and displayed. Disadvantageously, that system cannot determine the distance of an object from the screen.
Sharp Corporation has developed a bidirectional screen comprised of liquid crystal displays (LCDs) co-located at each pixel with optical sensors. Planar Corporation has also developed such a screen. In each case, that screen can determine the location of an object pressed against its surface, by detecting occlusion of light caused by the object. Disadvantageously, that screen cannot determine the distance of an object from the screen.